The present invention relates generally to photovoltaic (PV) power systems and, more particularly, to a PV power system that incorporates a set of hybrid DC contactors in order to provide for unique autonomous fault detection in individual PV strings or sub-arrays and a control system that employs logic for purposes of clearing faults and restoring healthy sub-arrays or PV strings.
PV power systems are power systems that employ a plurality of solar modules to convert sunlight into electricity. PV systems include multiple components, including photovoltaic modules, mechanical and electrical connections and mountings, and means of regulating or modifying the electrical output. One common arrangement in PV systems is for several PV modules to be connected in series to form a PV string, with multiple PV strings in a PV system then being combined in parallel to aggregate the current in a PV array. The PV modules generate direct current (DC) power, with the level of DC current being dependent on solar irradiation and the level of DC voltage dependent on temperature. When alternating current (AC) power is desired, an inverter is used to convert the DC energy from the array into AC energy, such as AC energy suitable for transfer to a power grid.
PV power systems also include a balance-of-system comprising DC switching and protection devices, combiner boxes, circuit breakers, disconnect switches, and contactors. Combiner boxes aggregate the DC power from the PV strings and provide a parallel connection point (i.e., a common bus) for the PV strings, with the combiner box providing overcurrent protection and isolation. Combiner boxes are either source combiners or array combiners, with source combiners being located closer to the PV strings and array combiners—or re-combiners—aggregating outputs from several source combiners into a single circuit.
It is recognized that there are several system design and component challenges associated with the operation of PV power systems. For example, overcurrent protection on a short circuit in the PV power system may have, at best, an over-current magnitude of 1.1× the rated current, thus making it impossible to provide over-current and short circuit detection and protection in PV power systems with conventional fuses and circuit breakers. Additionally, it is recognized that in a PV power system, a fault condition on a PV string is characterized by a current flow that is in a reverse direction from a current flow on a normally operating PV string, with the fault current also being many times greater than the current on a normally operating PV string (e.g., 1.1× with one parallel string to 100× when many parallel strings are present), such that traditionally there has not been a “one size fits all” solution to address such faults in a PV power system. Furthermore, existing switches in PV power systems cannot be automatically reset/reclosed after isolation of a faulted circuit so as to restore a circuit with healthy strings or combiner boxes—as would be desired in combiner boxes that are remote and not easily accessible. Another important function of the DC hybrid contactor is to integrate with arc-fault detection or ground fault detection methods and isolate the faulted sub-arrays/arrays. Breakers with shunt trips can be integrated but have the limitation of requiring a manual reset process. Still further, in existing PV power systems that employ conventional switches that cannot be remotely operated, it is not possible to continue to supply power in a PV system while the fault condition on a particular PV string is being addressed, such that the PV power system can continue to operate even while the fault is being addressed. This causes undesirable down time.
It would therefore be desirable to provide a PV power system and method for fault detection therein that provides over-current and short circuit detection with fault current and voltages specific to PV Systems and fault location with autonomous fault current direction detection and a DC remotely operated switch for isolating faulted circuit. It would further be desired to for such a PV system to provide the capability to remotely and/or automatically reclose contacts after isolating and restoring a faulted circuit and to continue to generate power while the faulted circuit is being addressed, such that the PV power system can continue to operate even while the fault is being addressed. It would further be desired for such a PV system to provide an enhanced level of service by integrating arc-fault detection, ground-fault detection, and leakage detection in floating arrays.